Locking Prop Fasteners

Homebuilt Aircraft & Kit Plane Forum

Help Support Homebuilt Aircraft & Kit Plane Forum:

memde

Member
Joined
May 2, 2020
Messages
8
We’re looking for some advice on a pusher prop installation, specifically how to prevent the nuts from coming loose.

As can be seen in the photos we have installed a ground adjustable E-Prop (NG-D 3-blade pusher) onto our electric motor. The install manual from E-Props does not mention anything about safety wire, just the required tightening torque and not to use loctite. All the installations we've seen (mostly on paramotors) show the prop bolts installed in the aft-to-fwd direction. Our installation requires that the prop bolts be installed in the opposite direction where the nuts are exposed instead of the bolt heads, which I think precludes us from using safety wire.

Does anyone have any recommendations as to a nut locking strategy in this application? Nylocks perhaps? Maybe through the resulting compression of the carbon hub, the tension on the bolts/nuts is such that our existing solution is ok? Something that's not too difficult to install and remove would be nice as we anticipate having to change the pitch often during flight tests to optimize performance. Thoughts?

Thanks.
E-Hawk Team
ehawk.iolani.org
 

Attachments

wsimpso1

Super Moderator
Staff member
Log Member
Joined
Oct 18, 2003
Messages
8,491
Location
Saline Michigan
Drilled nuts and safety wire works.

Drilled studs and castellated nuts and then either safety wire or cotter pins works.

Please look around at any maintenance shop at your local airport.
 

rv7charlie

Well-Known Member
Lifetime Supporter
Joined
Nov 17, 2014
Messages
2,174
Location
Pocahontas MS
The only reason that AC-43 (maintenance 'bible' from the FAA) gives for avoiding locknuts is when there's a risk of the bolted parts rotating *around the bolt*, which could provide loosening torque on the nut.

The only downside to Nyloc in that application might be temperature. FAA recommends avoiding their use in the engine compartment due to heat risk, though there are areas where they aren't heated enough to be a problem. I've used Nylocs on prop bolts on Lycomings for decades. If heat is a factor for you attached directly to the motor, then all-metal milspec lock nuts are available. If you have metric threads, you can still get both nylon and all-metal lock nuts, though I don't know of any milspec for them.

If you want to waste extra money to get the same job done, you could use Nord-lock (wedge-lock) washers.
 

Dana

Super Moderator
Staff member
Joined
Apr 3, 2007
Messages
10,230
Location
CT, USA
A lot of paramotors indeed use only bolts with no locking device. Seems sketchy, but I've never heard of one coming loose. In your case I think I'd use Nylocks. Remember to add the torque it takes to turn the nut alone to the final torque requirement.
 

memde

Member
Joined
May 2, 2020
Messages
8
Thanks for all the ideas.

I think the Nylocks could work as these bolts will not see temperatures anywhere close to something that could compromise the integrity of the nylon insert.

I had a look at distorted-thread locknuts but am concerned they could damage the bolt threads after multiple adjustments.

Another possible solution that I just came across would be safety wire with drilled nuts (see photo) however the only ones I have found so far of M8 size are titanium ($$$). I might have a go at drilling some myself using the mill.
 

Attachments

rv7charlie

Well-Known Member
Lifetime Supporter
Joined
Nov 17, 2014
Messages
2,174
Location
Pocahontas MS
BTW, your project a/c really looks interesting. If you can, ping us here with progress updates.

Charlie
 

memde

Member
Joined
May 2, 2020
Messages
8
BTW, your project a/c really looks interesting. If you can, ping us here with progress updates.

Charlie
Thanks for the link to the drill jig--will have to give it a try.

With regards to the current status of the project, I am in the process of recruiting new students as my last crew of students just graduated. In the near term, we will be concentrating our efforts in obtaining our airworthiness certificate. We are pretty good at updating our progress on our website blog (ehawk.iolani.org/blog) and on Instagram (ehawk_aircraft).
 

Geraldc

Well-Known Member
Joined
Nov 12, 2011
Messages
708
Location
nz
My E-Prop was supplied with Nord-lock washers and fitting instructions.
 

rv7charlie

Well-Known Member
Lifetime Supporter
Joined
Nov 17, 2014
Messages
2,174
Location
Pocahontas MS
If you don't want to invest in the drill jig, it is possible to grind a starting point for a drill bit using a small carbide burr in a Dremel tool, and drill the nut on a drill press. With care, you won't spend as much on bits as the jig costs. ;-)
 

Angusnofangus

Well-Known Member
Joined
Sep 29, 2015
Messages
561
Location
Victoria, Canada
If you don't want to invest in the drill jig, it is possible to grind a starting point for a drill bit using a small carbide burr in a Dremel tool, and drill the nut on a drill press. With care, you won't spend as much on bits as the jig costs. ;-)
Drilling nuts for safety wire requires something of a light touch. #50 drill bits want to break just as they are about to exit the hole. I got fairly good at it at one point, but it is still dicey.
 

Geraldc

Well-Known Member
Joined
Nov 12, 2011
Messages
708
Location
nz
All these comments are good aviation practice but when you buy a propeller from a reputable supplier why not use the supplied bolts and fasteners. They are part of the system and designed as such.
 

Marc Zeitlin

Exalted Grand Poobah
Joined
Dec 11, 2015
Messages
1,034
Location
Tehachapi, CA
I think the Nylocks could work as these bolts will not see temperatures anywhere close to something that could compromise the integrity of the nylon insert.
While that's true, nylon insert nuts are not as good at holding torque as the all-metal locknuts such as MS21042 or AN363, and wear out faster, in my experience.

I had a look at distorted-thread locknuts but am concerned they could damage the bolt threads after multiple adjustments.
Generally doesn't happen - if anything wears out or loses prevailing torque, it's the nut, not the bolt.

Another possible solution that I just came across would be safety wire with drilled nuts (see photo) however the only ones I have found so far of M8 size are titanium ($$$). I might have a go at drilling some myself using the mill.
So you've gotten a lot of comments regarding safety wiring. But unless I'm misunderstanding what your system is, you've got bolts that can turn in the through holes, not studs that are fixed. Yes? If that's true, then safetying the nuts to each other accomplishes exactly nothing whatsoever, since the bolt is still free to turn. Safety wire is only useful when one end of the threaded system can't move, and the safety wire prevents the 2nd end from moving. If BOTH ends can move, then the safety wire can't accomplish anything.

In a case like this, if you want belt and suspenders, the Nord-Locks and a metal locking nut are about as much security for these bolts as can be obtained. But I'd go with just the metal locking washers also - the NL's would be overkill if you're using metal locking washers.
 

memde

Member
Joined
May 2, 2020
Messages
8
All these comments are good aviation practice but when you buy a propeller from a reputable supplier why not use the supplied bolts and fasteners. They are part of the system and designed as such.
We are using the manufacturer supplied fasteners. It just seemed odd that there was no locking mechanism specified. Maybe they just don't come loose if properly torqued as others using the same prop have mentioned. Thanks for the video on the nord-locks. We happen to be using them for our battery terminal connections.
 

Attachments

memde

Member
Joined
May 2, 2020
Messages
8
While that's true, nylon insert nuts are not as good at holding torque as the all-metal locknuts such as MS21042 or AN363, and wear out faster, in my experience.

Generally doesn't happen - if anything wears out or loses prevailing torque, it's the nut, not the bolt.

So you've gotten a lot of comments regarding safety wiring. But unless I'm misunderstanding what your system is, you've got bolts that can turn in the through holes, not studs that are fixed. Yes? If that's true, then safetying the nuts to each other accomplishes exactly nothing whatsoever, since the bolt is still free to turn. Safety wire is only useful when one end of the threaded system can't move, and the safety wire prevents the 2nd end from moving. If BOTH ends can move, then the safety wire can't accomplish anything.

In a case like this, if you want belt and suspenders, the Nord-Locks and a metal locking nut are about as much security for these bolts as can be obtained. But I'd go with just the metal locking washers also - the NL's would be overkill if you're using metal locking washers.
Thanks for the info. Regarding the bolts, they are held captive in the prop adapter plate (see photo) which may not have been obvious from the photos I attached. I think we'll go with either the metal locking washers or nord-locks (not both) and monitor the situation as we begin some high power ground runs.
 

Attachments

Top